Monitoring of vapor density in vapor deposition furnance by emission spectroscopy

ABSTRACT

The rate of vapor deposition in a vacuum furnace heated by electron bombardment is monitored or controlled. The vapor is ionized, preferably by the same electron bombardment as produces it. The ionized vapor radiates light which is detected at one or more locations within the furnace, preferably by a photomultiplier optically coupled by a light pipe to the interior of the furnace. The light detector produces a signal indicative of the intensity of the light detected and, hence, of the vapor density. Optical filters may be used to pass light of frequency characteristic of particular elements, so that the relative intensity of the particular elements in the vapor may be selectively detected. The signals may be recorded or used to control the heating and, hence, vapor density, as by controlling the electron emission from an electron gun.

United States Patent Inventor s Rome h,.1r- Blankenship 118/7 3,168,418 2/1965 Payne 118/7 1 1 pp 590,736 2,952,776 9/1960 Schumacher et al. 250/435 [2 1 Filed 091-31, 1966 2,285,564 6 1942 Brooke et a1. 250/218 1 Patented ep 1971 2,885,926 5/1959 Mo1loy.. 88/14 1 Assisnee Reduction p y Incorporated 3,051,035 8/1962 Root 250/227 3,207,996 9/1965 Sundstrom 88/14 Primary Examiner-Walter Stolwein [54] MONITQRING PO EN Y 1 VAPOR Attorney-Anderson, Luedeka, Fitch, Even & Tabin DEPOSITION FURNANCE BY EMISSION SPECT-ROSCOPY ABSTRACT: The rate of vapor deposition in a vacuum fur- 11 Claims, 1 Drawing Fig.

nace heated by electron bombardment is monitored or con- U-S. trolled The vapor is ionized preferably the ame electron 250/213, bombardment as produces it. The ionized vapor radiates light [51 1 [I ll- Cl. G02 1/28 which is detected at one or more locations within the furnace, of Search preferably a photomultiplier optically coupled a 49-5, 215, 145 145 pipe to the interior of the furnace. The light detector produces 148 356/87 a signal indicative of the intensity of the light detected and, hence, of the vapor density. Optical filters may be used to pass [56] Rem-mes Cited light of frequency characteristic of particular elements, so that UNITED STATES PATENTS the relative intensity of the particular elements in the vapor 7 3,213,747 /1965 Van Der Smissen 356/87 may be selectively detected. The signals may be recorded or 3,373,278 3/1968 Cilyo 250/495 used to control the heating and, hence, vapor density, as by 2,410,104 10/1946 Rainey 250/227 controlling the electron emission from an electron gun.

msunnrl 3.88 67 5 I POHER 5b f su m 38 Szwzcxlgxs L V fi 7 51 y 712 cannot-I. van/w: 73 f sou/wt 2 N arm-macs AMPLIFIER MONITORING OF VAPOR DENSITY IN VAPOR DEPOSITION FURNANCE BY EMISSION SPECTROSCOPY The present invention relates generally to a means for monitoring vapor density in a high-vacuum electron beam furnace and more particularly to an improved method and apparatus for accurately measuring the density of vapor at predetermined locations. in a high-vacuum electron beam furnace by emission spectroscopy.

Numerous industrial processes using various vaporization techniques are becoming increasingly useful. For example, such processes are employed to great advantage in the deposition of very thin films of both metallic and metallic materials on a wide variety of substances. Apparatus using electron beams as a source of heat are particularly useful in such processes, since the extremely high power densities attainable, makes the selection of materials which are to be melted and evaporated virtually limitless. Typically, a beam of electrons is generated by the heated filament, of an electron gun in a high-vacuum electron beam furnace. The electron beam is directed onto the evaporant material and melts it. Continued heating vaporizes the evaporant material. A water-cooled crucible may be employed when a high melting point material is to be evaporated, thereby preventing a reaction between the crucible itself and the evaporant.

Preferably a magnetic field is generated adjacent the crucible for directing the beam of electrons onto the evaporant. This magnetic field is preferably directed perpendicular to the direction of travel of the electrons and, hence, deflects them into a curved path. The use of a magnetic field for directing the electrons onto the evaporant permits the positioning of the electron gun in an area isolated from the vapors produced. This prevents the electron-emitting apparatus from being contaminated by the vapors. It is usually possible to obtain vapor pressures as high as several millimeters of mercury in the region relatively close to the evaporant without adversely affecting the associated equipment by using this method of focusing the electron beam. A relatively dense vapor cloud of this nature is desirable in order to produce relatively high rates of vapor plating.

When the beam of electrons, which may be designated as primary electrons, is directed into the cloudsof vapor, a rather small percentage of the electrically neutral atoms in the cloud are subjected to bombardment by the primary electrons. As a result of such bombardment previously electrically neutral molecules become ionized by the knocking off of an electron from an atomic orbit. Such electrons may be designated as secondary electrons. These secondary electrons dislodged as a result of the ionizing collisions acquire some kinetic energy in the process. Secondary electrons may also be produced by the primary electrons impinging upon the evaporant.

The emitted or secondary electrons generally move quite Slowly relative to the primary electrons. Since these electrons travel more slowly they require more time to pass through or adjacent to the electric fields of the other neutral atoms in the vapor cloud. Consequently, these secondary electrons are better able to afi'ect the electrons in the outer electron shells of the neutral atoms and thereby are more effective for ionizing neutral atoms than are the faster moving primary electrons, provided, of course, that the secondary electrons have sufficient energy to overcome the binding energy binding the electrons to the atom.

The more slowly moving secondary electrons which result from the ionization process previously described are also more greatly deflected by magnetic lines of force as they move through a magnetic field than are the faster moving (higher energy) primary electrons. The paths of the secondary electrons are thus curved very sharply by the magnetic field relative to the effect experienced by the primary electrons. As a result, low-energy electrons can be virtually trapped by the magnetic field, while the high energy primary electrons are deflected only enough to cause them to strike the evaporant.

The only escape route from the vapor cloud for these secondary electrons is in a generally spiral path toward a pole piece of the magnet. This spiral path of the secondary electrons is substantially longer than the path of the primary electrons, and hence increases the possibility of producing additional ions at the secondary electrons travel through the magnetic field.

Often a single electron released as a result of an ionizing collision is given sufficient kinetic energy to effect the formation of several additional ions and liberate the associated electrons before passing out of the magnetic field. Each ionizing collision results in the loss of kinetic energy by the electron equal to the ionizing potential of the particular atom involved. For example, if a cloud vapor comprises copper atoms it is theoretically possible for a electron volt primary electron to generate 12 copper ions, the ionizing potential of copper being 7.723 electron volts. As a practical matter, however, it has generally been found that only about half the ionization is produced as is theoretically predicated, for moderate densities at about i millimeter of mercury.

ln addition to creating further ionization by knocking electrons completely free of their molecules, the primary and secondary electrons may lose energy to the atoms without freeing an electron. When an electron undergoes such an inelastic interaction with an atom, the electron excites the atom, changing its electronic energy state to a higher level, the electron losing kinetic energy in the process. The atom thereupon emits a predetermined amount of energy in the form of radiation as an orbital electron returns to its lower level.

The wave length of the radiation emitted is predictable from a knowledge of the type of atom involved and the change in its energy state. The substances of interest for purposes of the present application generally emitenergy in the form of light waves in the visible or ultraviolet range. A spectral analysis of the emitted radiation may be carried out by using appropriate filters and aligning a photosensitive device such as a photomultiplier tube to receive the filtered light waves. The photomultiplier produces an electrical signal systematically related to the quantity of light impinging on its photosensitive cathode, thereby providing an indication of the vapor density of particular materials.

It is readily apparent that the higher the vapor density the greater the number of inelastic interactions or collisions and thus the greater the amount of emitted light for a given quantity of primary electronsvor initial electron beam current. This principle may be readily applied to monitor continuously the density of the vapor in a highvacuum electron beam furnace as well as for other uses. Alternatively, a portion of the electrical signal produced by the photomultiplier may be fed back to the power supply which controls the power output of the electron gun, thereby regulating the intensity of the electron beam so that a predetermined quantity of vapor is continuously present. Also a selective filtering device may be operated periodically to transmit selectively, light having different predetermined wave lengths of interest to the photosensitive device, thereby obtaining a measure of the relative quantities of a plurality of particular elements present in the evaporant material. In addition, it is possible to scan various regions of the vapor cloud to obtain a convenient detennination of the vapor distribution.

Accordingly, it is an object of the present invention to provide an accurate means for continuously monitoring the density of vapor in a high-vacuum electron beam apparatus. It is another object of the present invention to provide a means for accurately determining the relative quantities of material present in a particular vapor. It is another object of the present invention to provide a means for determining the relative distribution density of vaporous material in a high-vacuum electron beam apparatus. It is another object of the present invention to provide a means for continuously monitoring the vapor density in a high-vacuum electron beam apparatus and employing the thus obtained information for maintaining the vapor density substantially constant. It is still a further object of the present invention to provide a means for measuring the vapor density adjacent a source of evaporant in a high-vacuum electron beam furnace by emission spectroscopy. Other objects and advantages of the present invention will become apparent from the following description and accompanying drawing, wherein:

The single FIGURE is a schematic view of a preferred embodiment of the present invention.

Referring to the drawing, an apparatus in accordance with the present invention generally includes a light-receiving means or light pipe disposed a predetermined distance from a crucible 12 containing evaporant 14, and in optical communication with the emitted vapors 15. A' relatively narrow band pass light filter means 18, adapted for transmitting particular spectral band widths of interest while filtering out or blocking background light along with other undesired light waves, is disposed between the light pipe 10 and a second light pipe 22 which passes the light spectrum transmitted by the filter 18 to a photosensitive device 26.

The present invention is particularly adaptable for use in conjunction with a high-vacuum electron beam apparatus, where the metallic vapor environment makes conventional methods of monitoring vapor density unsuitable. In such apparatus a quantity of a suitable evaporant material 14 such as aluminum, copper etc. is usually disposed in the crucible 12 positioned within a conventional high-vacuum electron beam furnace 34. It is generally preferable to provide cooling means for the crucible structure so as to prevent reaction between the crucible l2 and the evaporant material 14. A liner 36 of refractory material may be interposed between the hot evaporant l4 and the cooler crucible 12 so that the crucible may be kept cool enough to remain solid while the evaporant is melted and vaporized. In this connection a plurality of water coolant tubes 38 are usually provided adjacent the crucible structure.

An electron gun 42, including an electron-emitting filament cathode 44 and an accelerating anode 46, is disposed within the electron beam furnace 34 and is connected to a conventional electron gun power supply 50. The electron gun 42 is adapted for producing a beam of electrons of a desired intensity varying in accordance with the current supplied to its cathode 44 by the power supply 50, for melting and vaporizing a particular target material. Preferably the electron gun 42 is disposed at a predetermined distance from the evaporant material 14 in the crucible 12 and out of the path of the vapors 15. This precludes contamination of the electron-emitting cathode 44 by the vaporous material produced as previously mentioned.

The beam of electrons generated by the electron gun 42 is directed transversely into a magnetic field, established adjacent the electron gun 42 by an appropriate magnet means 51. The magnet means 51 generates a magnetic field having lines of force generally normal to the plane of the drawing, which field deflects the electron beam as shown. The magnetic field thus deflects the beam of electrons onto the evaporant 14 contained within the crucible 12. By appropriately regulating the intensity of the electron beam, the evaporant 14 is vaporized and relatively dense clouds of vapor are thus created adjacent the surface of the crucible 12. By appropriate shaping of the surfaces within the crucible, the vapor is directed outwardly from the crucible 12 against a substrate 52, where the vapors condense to coat the substrate 52 with the evaporated evaporant material 14.

As previously explained, the inelastic interactions of electrons within the vapor cloud results in the emission or radiation throughout the vapor cloud, varying in intensity with the density of the vapor and varying in wavelength in accordance with the type of atoms comprising the vapor. For example, if relatively pure aluminum is employed as the evaporant material, light waves having a peak intensity at a wavelength of approximately 3,960 angstroms are emitted. This wavelength is a particular characteristic of the element aluminum. Each element has associated with it a known characteristic spectrum, which may be determined by reference to scientific tables such as those found in Pearse, R.W.B., and A.G. Gaydon The Identification of Molecular Spectra, Chapman & Hall, Ltd., London, Third Edition, 1963.

The light pipe 10 is disposed such that it extends into the furnace 34. Preferably the light pipe 10 has an open end 53 which is disposed at a predetermined distance from the evaporant 14 and its associated cloud of vapor 15 or plasma. The light pipe 10 essentially comprises a relatively short straight piece of hollow tubing preferably fabricated of a relatively noncorrodible material. At its end opposite to the open end 53, the light pipe 10 is preferably optically coupled to the light filter 18 through a transparent window 54.

In this connection, it is generally desirable to provide a means for preventing undue clouding of the window 54 by the vapor molecules. This is conveniently accomplished by the provision of an apparatus generally similar to that disclosed in Hunt U.S. Pat. No. 3,170,383 which issued on Feb. 23, 1965. Accordingly, a very small quantity of a nonreactive gas such as nitrogen is introduced into the light pipe 10 adjacent the window 54 through an inlet tube 56. Since the furnace 34 is maintained at at extremely high vacuum, a pressure gradient is established within the pipe 10 such that the gas introduced flows toward the open end 53 of the pipe 10. In so doing, vapor molecules collide with the molecules of nitrogen gas, and are deflected out of the pipe 10 or onto the walls of the pipe where they condense, without reaching the surface of the window 54.

Preferably the light filter 18 is selected such that it transmits predetermined spectral band widths of interest and blocks or filters out extraneous light such as that present in the background. For example, if the evaporant is aluminum and it is desired to monitor the vapor density present, the filter 18 is selected to transmit light having a wavelength of approximately 3,960 angstroms.

The second light pipe 22 is coupled to the output end of the filter 18, and is in optical communication with the first light pipe 10, for receiving the collimated light transmitted through the first light pipe 10. This is often accomplished by merely aligning the second light pipe 22 with the first light pipe 10. But, in certain instances the filter 18 may diffract or bend the light which it transmits. In such cases the second light pipe 22 is merely appropriated positioned such that it receives the diffracted light.

The light pipe 22 is optically coupled to the photosensitive device 26, which preferably comprises a conventional photomultiplier tube. The photosensitive device is selected to have an appropriate spectral response; it is preferably selected to have its peak sensitivity in the portion of the spectrum that is of interest. A power supply 60 is coupled to the photomultiplier tube 26 is adapted for rendering it operable. The photomultiplier tube 26 is adapted for generating an electrical signal systematically related to the intensity of the light impinging on its photocathode. Preferably a photomultiplier is selected which exhibits a substantially linear response over a relatively wide range of impinging intensities of light.

The output signal generated by the photomultiplier tube 26 may be monitored by a suitable meter or a recording device, thereby yielding an indication of the vapor density present in the region of the vapor cloud 15 adjacent the first light pipe 10.

[n a preferred embodiment of the present invention, the output signal produced by the photomultiplier tube 26 on an output resistor 64 is supplied to a suitable amplifier 68, which may be a conventional amplifier circuit capable o amplifying an electrical signal of several tenths of a volt and include a conventional cathode follower circuit.

The amplifier output signal produced by the amplifier 68 is systematically related to the vapor density in the furnace 34. Thus, a suitable meter 70, such as an oscilloscope or a recording device is preferably connected to the output of the amplifier 68 to yield an indication of the output signal and consequently a quantitative measurement of the vapor density in the furnace 34.

In certain applications it is advantageous to feed back a predetermined portion of the amplified output signal to control the output of power supply 50. This feedback signal may be utilized to adjust the output of the power supply, which in turn controls the current supplied to the electron emitting filament cathode, thereby adjusting the intensity of the electron beam generated, and correspondingly regulating the vapor density in the furnace 34. The feedback signal may be developed by comparing the signal from cathode follower 68 with a reference signal from a reference voltage source 72 which may, as shown, comprise a potentiometer 74 connected to a fixed voltage as supplied by a fixed voltage source 76. The comparison is effected by applying both signals to respective inputs of a difference amplifier 78 which produces a signal proportional to the difference between the two signals. The difference signal is thus indicative of how far the detection signal differs from the reference signal which may be set by adjustment of the potentiometer 74. The difference signal may be applied over a conductor 80 to a gun filament controller 82 which operates in a conventional manner to control how much current is supplied from the power supply 50 to the filament cathode 44 of the electron gun 42, thus controlling the intensi ty of the electron beam current. The controller 82 varies the filament current in such manner as to reduce the difference signal toward null. For example, if a positive difference signal is produced when the detection signal is larger than the reference, the filament current is reduced, thereby reducing the intensity of the electron beam and hence the vapor density. This results in a reduction in the detection signal. If there is sufficient gain in the system, the vapor density will be reduced until the detection signal at the output of the cathode follower 68 is just equal to the selected reference signal as produced by the potentiometer 74.

As an alternative the voltage output of the power supply 50 can be controlled to control the accelerating voltage of the electron gun, thereby controlling its power output and the heating energy transferred. Either system provides a highly sensitive control of the density of vapor at predetermined locations within the furnace 34 and yields a relatively convenient means for maintaining the evaporation rate at a desired value. Of course, any change in the intensity of the primary electron beam not only changes the vapor density but also the degree of ionization thereof, thus directly affecting the measured light intensity. Nevertheless, if the light intensity is maintained constant at the desired level by controlling the primary beam, the vapor density is maintained constant. The relationship between light intensity and vapor density may be determined empirically should it be desirable to calibrate the control.

If desired, the present invention may be readily adapted for continuously monitoring the relative quantities of the various materials comprising the vapor. For example, such a means for precisely monitoring the composition of the vapor cloud is quite useful in indicating what substances are to be added to the evaporant 14 so as to maintain a desired predetermined composition of material in the vapor. This relative quantity monitoring function may be conveniently provided by adapting the filter 18 for sequential filtering operation. A programmer 84 may operate to change the filter band automatically. The programmer 84 may be in the nature of a clock periodically producing operating voltage for a motor 85 which is energized periodically. The motor 85 is coupled by a shaft 86 to a disc 87 upon which is mounted a plurality of filter elements, each passing respective selective frequencies. The program 84 therefore operates the motor 85 periodically rotating the disc 87 to place respective filter elements into operating position.

As previously discussed, each of the elements of interest which is being monitored emits a characteristic light wave having an intensity indicative of the quantity of the particular substance in the vapor cloud. Thus, the sequential filter is preferably operated to pass predetermined band widths periodically, each containing particular respective wave lengths of interest. By appropriately programming the sequential filter, the relative quantities of a substantial number of different substances present in the vapor cloud may be readily obtained. In such cases it may be desirable to use as meter 70 a multichannel recorder synchronized by the programmer 84. This in turn provides a highly useful means for obtaining a precise indication of changes in the composition of the evaporant as indicated by the relative percentages of vaporized material present in the vapor cloud 15. Thus, if desired, needed additions may be made to the evaporant to maintain the composition in a predetermined state.

In certain instances, the present invention may be readily adapted for accurately indicating the distribution of the vapor at predetermined locations. In this connection the light pipe 10 may be mounted in a ball and socket joint 90, permitting the open end 53 of the light pipe 10 to be conveniently directed at various locations within the enclosure 34. Other parts of the monitor apparatus must, of course, be mounted to pivot with the light'pipe 10.

As previously described, the evaporant 14 contained in the crucible l2 and is bombarded by the high-energy electron beam, resulting in the vaporization of the material. The vaporized material rises from the surface of the crucible 12 forming a cloud of vapor 15. In ascertaining the density distribution of such a vaporous cloud it is generally preferable to scan the cloud by taking a series of intensity readings along various planes through the cloud. By virtue of such readings an accurate indication of the distribution of the vapor density throughout the cloud of vapor is provided.

Thus, a highly useful and convenient method and apparatus has been provided for yielding an indication of the vapor density present in a high-vacuum electron beam apparatus. in addition, several illustrative examples have been set forth indicating some of the numerous uses for such an apparatus. These examples are merely intended as illustrations and are not intended to limit the scope of the invention.

For example, it has been found in operation that in certain applications, particularly when evaporating highly reflecting metals, background light from reflecting surfaces in the furnace 34 causes problems in obtaining reproducible and consistent measurements. To overcome this the photosensitive device 26 may be aligned with a closed end tube 92 located on the other side of the vapor cloud. The tube 92 is coated with a nonreflecting coating on its interior which effectively acts as a nonreflecting black hole and which thus serves to stabilize the measurement.

Various other changes and modifications may be made in the above-described apparatus without deviating from the spirit or scope of the present invention. Various features of the present invention are set forth in the following claims.

lclaim:

1. Apparatus for depositing vapor on a substrate including a high vacuum electron beam furnace for generating vapor by subjecting an evaporant material to intense heating by the injection of a beam of high-velocity electrons into said evaporant material, said vapor thereupon emanating from the surface of said evaporant material and passing into the beam of electrons where a portion of the particles of vapor is ionized by the action of electrons in said beam, in combination with measuring apparatus comprising photosensitive means in optical communication with said vapor thus ionized and responsive to the intensity of light from said vapor by producing an electrical signal systematically related to the intensity thereof, and means coupled to an output of said photosensitive means for recording said electrical signal, thereby providing a measure of the density of said vapor thus ionized.

2. The apparatus of claim 1, wherein said measuring apparatus includes a light-collimating means comprising a hollow tube having an open end in optical communication with said vapor particles.

3. Apparatus for depositing vapor on a substrate including a high-vacuum electron beam furnace for generating vapor by subjecting an evaporant material to intense heating by the inabundance of predetermined materials in the vapor comprisjection of a beam of high-velocity electrons onto the surface of said evaporant material, said vapor thereupon emanating from said surface and passing into the beam of electrons where a portion of the particles of vapor is ionized by the action of electrons is said beam with the consequent emission of light of frequency characteristic of the elemental constitution of the vapor, in combination with measuring apparatus comprising light receiving means in optical communication with said vapor, light filter means coupled to said light receiving means for passing light of predetermined frequency, light sensitive means coupled to said light filter means, said light sensitive means being responsive to the intensity of the light reaching it by producing an electrical signal systematically related thereto, and means coupled to an output of said light sensitive means for recording said electrical signal, thereby providing a measure of the density of vapor emitting light of the frequency passed by said light filter means.

4. Apparatus for the controlled deposition of vapor on a substrate including a high-vacuum electron beam furnace for generating vapor by subjecting an evaporant material to electron bombardment heating by the injection of a beam of highvelocity electrons emitted by an electron gun onto the surface of said evaporant material, said vapor thereupon emanating from said surface and passing into the beam of electrons where a portion of the particles of vapor is ionized by the action of electrons in said beam with the consequent emission of light of frequency characteristic of the elemental constitution of the vapor and intensity dependent upon the density of the vapor, in combination with apparatus for controlling the abundance of vapor thus generated comprising light receiving means in optical communication with said vapor, photosensitive means optically coupled to said light receiving means, said photosensitive means being responsive to the intensity of the light reaching it by producing an electrical signal systematically related thereto, and means coupled to the output of said photosensitive means for controlling the intensity of the beam of electrons from said electron gun in accordance with said electrical signal.

5. Apparatus for the controlled deposition of vapor on a substrate including a high-vacuum electron beam furnace for generating vapor by subjecting an evaporant material to electron bombardment heating by the injection of a beam of highvelocity electrons emitted by an electron gun onto the surface of said evaporant material, said vapor thereupon emanating from said surface and passing into the beam of electrons where a portion of the particles of vapor is ionized by the action of electrons in said beam with the consequent emission of light of frequency characteristic of the elemental constitution of the vapor and intensity dependent upon the density of the vapor, in combination with apparatus comprising a hollow tube having an open end in optical communication with said vaporous material and having a transparent window at its opposite end, an optical filter optically coupled to said hollow tube through said window for passing light waves of predetermined frequency, a photomultiplier tube optically coupled to said hollow tube through said filter, said photomultiplier tube being responsive to the intensity of the light reaching it by producing an electrical signal systematically related thereto, and means coupled to the output of said photomultiplier tube for maintaining the vapor at a predetermined density.

6. For depositing vapor on a substrate, a method for produc ing vapor and spectroscopically monitoring the density thereof comprising subjecting an evaporant material to electron bombardment heating in a high-vacuum electron beam furnace to produce vapor particles of such material, ionizing at least a portion of said particles to produce light of intensity dependent upon the density of said vapor and of frequency dependent upon its elemental constitution, and separately de- 70 tecting the intensity of light of frequency characteristic of a particular element by producing electrical signals systematically related thereto.

7. For depositing vapor on a substrate, a method for producing vapor and spectroscopically indicating the relative ing subjecting an evaporant material to electron bombardment heating in a high-vacuum electron beam furnace to produce vapor particles of such material, ionizing at least a portion of the particles of the vapor to produce light of intensity dependent upon the density of said vapor and of frequency dependent upon its elemental constitution, collimating a portion of said light, sequentially filtering said collimated light to transmit particular respective frequencies cyclically, and separately detecting the intensity of said collimated light at said respective cyclically transmitted frequencies as an indication of the relative abundance of particular elements in said vapor by producing electrical signals systematically related thereto.

8. For depositing vapor on a substrate, a method for producing vapor and monitoring the abundance thereof comprising subjecting an evaporant material to electron bombardment heating in a high-vacuum electron beam furnace to produce vapor particles of such material, directing primary electrons into the vapor and magnetically deflecting said primary electrons and the secondary electrons produced in the vapor by said primary electrons to ionize at least a portion of the particles of said vapor to produce light of intensity dependent upon the density of said vapor, and detecting the intensity of such light as an indication of the abundance of vapor by producing electrical signals systematically related thereto.

9. For depositing vapor on a substrate, a method for producing vapor and monitoring the abundance thereof comprising subjecting an evaporant material to electron bombardment heating in a high-vacuum electron beam furnace to produce vapor particles of such material, ionizing at least a portion of the particles of said vapor to produce light of intensity dependent upon the density of said vapor and of frequency dependent upon its elemental constitution, and detecting the intensity of light of frequency characteristic of a particular element at predetermined locations as an indication of the abundance of particular elements in said vapor at said locations by producing electrical signals systematically related thereto.

10. For the controlled deposition of vapor on a substrate, a method for producing vapor and controlling the abundance thereof comprising subjecting an evaporant material to electron bombardment heating in a highvacuum electron beam furnace by injecting a beam of high-velocity electrons by an electron gun onto the surface of said evaporant material thereby causing vapor particles of such material to emanate from said surface and pass into the beam of electrons, ionizing a portion of the particles of vapor by the action of electrons in said beam such that light is emitted having an intensity dependent upon the density of the vapor, transmitting a predetermined portion of said emitted light, detecting said transmitted light by producing an electrical signal systematically related to the intensity of said transmitted light, and applying said electrical signal to control the intensity of the electron beam from said electron gun, thereby controlling the abundance of vapor generated.

11. For the controlled deposition of vapor on a substrate, a method for producing vapor and controlling the abundance i thereof comprising subjecting an evaporant material to electron bombardment heating in a high-vacuum electron beam furnace by injecting a beam of high-velocity electrons by an electron gun onto the surface of said evaporant material thereby causing vapor particles of such material to emanate from said surface, ionizing a portion of the particles of vapor by the action of electrons in said beam such that light is emitted having a frequency characteristic of the elemental constitution of the vapor and having an intensity dependent upon the density of the vapor, passing a portion of said emitted light through a light pipe disposed in optical communication with said vapor, filtering said passed light such that light of predetermined frequency is transmitted, detecting said transmitted light by producing an electrical signal systematically related to the intensity of the transmitted light, and utilizing said electrical signal to control the intensity of the electron beam from said electron gun, thereby maintaining the abundance of vapor at a predetermined level.

Patent No. 3 ,609, 378

Inventor (s) Hugh ROSC In the title Column 1, line 14,

Column 4, line 52,

Column 6, line 22,

Claim 3, Column 7,

Claim 6, Column 7,

Claim 7, Column 8,

Claim 9, Column 8,

(SEAL) Attest:

EDWARD l LFLE'PcHER; JR-

Attesting Officer ORM PC3-1050 (10-69) "FURNANCE" UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Dated Segtember 28, 1971 oe Smith, Jr.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

should read --FURNACE "metallic and metallic" should read --metallic and nonmetallic- "tube 26 is adapted for rendering" should read -tube 26 for rendering-- "crucible l2 and is bombarded" should read -crucible 12 is bombarded-- line 5, delete is and insert --in-- lines 67 and 68, after "ionizing" insert --with said beam-- line 4, after "vapor" insert -with said beam line 31, after "ionizing" insert -with said beam-- Signed and sealed this 9th day of May 1972.

ROBERT (HIIIZIIESHHALK Commissioner of Patents USCOMM-DC 60376-P69 Q U S GOVERHMiNT PRINTlNG OFFICE I959 O355-334 

2. The apparatus of claim 1, wherein said measuring apparatus includes a light-collimating means comprising a hollow tube having an open end in optical communication with said vapor particles.
 3. Apparatus for depositing vapor on a substrate including a high-vacuum electron beam furnace for generating vapor by subjecting an evaporant material to intense heating by the injection of a beam of high-velocity electrons onto the surface of said evaporant material, said vapor thereupon emanating from said surface and passing into the beam of electrons where a portion of the particles of vapor is ionized by the action of electrons in said beam with the consequent emission of light of frequency characteristic of the elemental constitution of the vapor, in combination with measuring apparatus comprising light receiving means in optical communication with said vapor, light filter means coupled to said light receiving means for passing light of predetermined frequency, light sensitive means coupled to said light filter means, said light sensitive means being responsive to the intensity of the light reaching it by producing an electrical signal systematically related thereto, and means coupled to an output of said light Sensitive means for recording said electrical signal, thereby providing a measure of the density of vapor emitting light of the frequency passed by said light filter means.
 4. Apparatus for the controlled deposition of vapor on a substrate including a high-vacuum electron beam furnace for generating vapor by subjecting an evaporant material to electron bombardment heating by the injection of a beam of high-velocity electrons emitted by an electron gun onto the surface of said evaporant material, said vapor thereupon emanating from said surface and passing into the beam of electrons where a portion of the particles of vapor is ionized by the action of electrons in said beam with the consequent emission of light of frequency characteristic of the elemental constitution of the vapor and intensity dependent upon the density of the vapor, in combination with apparatus for controlling the abundance of vapor thus generated comprising light receiving means in optical communication with said vapor, photosensitive means optically coupled to said light receiving means, said photosensitive means being responsive to the intensity of the light reaching it by producing an electrical signal systematically related thereto, and means coupled to the output of said photosensitive means for controlling the intensity of the beam of electrons from said electron gun in accordance with said electrical signal.
 5. Apparatus for the controlled deposition of vapor on a substrate including a high-vacuum electron beam furnace for generating vapor by subjecting an evaporant material to electron bombardment heating by the injection of a beam of high-velocity electrons emitted by an electron gun onto the surface of said evaporant material, said vapor thereupon emanating from said surface and passing into the beam of electrons where a portion of the particles of vapor is ionized by the action of electrons in said beam with the consequent emission of light of frequency characteristic of the elemental constitution of the vapor and intensity dependent upon the density of the vapor, in combination with apparatus comprising a hollow tube having an open end in optical communication with said vaporous material and having a transparent window at its opposite end, an optical filter optically coupled to said hollow tube through said window for passing light waves of predetermined frequency, a photomultiplier tube optically coupled to said hollow tube through said filter, said photomultiplier tube being responsive to the intensity of the light reaching it by producing an electrical signal systematically related thereto, and means coupled to the output of said photomultiplier tube for maintaining the vapor at a predetermined density.
 6. For depositing vapor on a substrate, a method for producing vapor and spectroscopically monitoring the density thereof comprising subjecting an evaporant material to electron bombardment heating in a high-vacuum electron beam furnace to produce vapor particles of such material, ionizing with said beam at least a portion of said particles to produce light of intensity dependent upon the density of said vapor and of frequency dependent upon its elemental constitution, and separately detecting the intensity of light of frequency characteristic of a particular element by producing electrical signals systematically related thereto.
 7. For depositing vapor on a substrate, a method for producing vapor and spectroscopically indicating the relative abundance of predetermined materials in the vapor comprising subjecting an evaporant material to electron bombardment heating in a high-vacuum electron beam furnace to produce vapor particles of such material, ionizing at least a portion of the particles of the vapor with said beam to produce light of intensity dependent upon the density of said vapor and of frequency dependent upon its elemental constitution, collimating a portion of said light, sequentially filtering said collimated light to transmit particular respective frequencies cycliCally, and separately detecting the intensity of said collimated light at said respective cyclically transmitted frequencies as an indication of the relative abundance of particular elements in said vapor by producing electrical signals systematically related thereto.
 8. For depositing vapor on a substrate, a method for producing vapor and monitoring the abundance thereof comprising subjecting an evaporant material to electron bombardment heating in a high-vacuum electron beam furnace to produce vapor particles of such material, directing primary electrons into the vapor and magnetically deflecting said primary electrons and the secondary electrons produced in the vapor by said primary electrons to ionize at least a portion of the particles of said vapor to produce light of intensity dependent upon the density of said vapor, and detecting the intensity of such light as an indication of the abundance of vapor by producing electrical signals systematically related thereto.
 9. For depositing vapor on a substrate, a method for producing vapor and monitoring the abundance thereof comprising subjecting an evaporant material to electron bombardment heating in a high-vacuum electron beam furnace to produce vapor particles of such material, ionizing with said beam at least a portion of the particles of said vapor to produce light of intensity dependent upon the density of said vapor and of frequency dependent upon its elemental constitution, and detecting the intensity of light of frequency characteristic of a particular element at predetermined locations as an indication of the abundance of particular elements in said vapor at said locations by producing electrical signals systematically related thereto.
 10. For the controlled deposition of vapor on a substrate, a method for producing vapor and controlling the abundance thereof comprising subjecting an evaporant material to electron bombardment heating in a high-vacuum electron beam furnace by injecting a beam of high-velocity electrons by an electron gun onto the surface of said evaporant material thereby causing vapor particles of such material to emanate from said surface and pass into the beam of electrons, ionizing a portion of the particles of vapor by the action of electrons in said beam such that light is emitted having an intensity dependent upon the density of the vapor, transmitting a predetermined portion of said emitted light, detecting said transmitted light by producing an electrical signal systematically related to the intensity of said transmitted light, and applying said electrical signal to control the intensity of the electron beam from said electron gun, thereby controlling the abundance of vapor generated.
 11. For the controlled deposition of vapor on a substrate, a method for producing vapor and controlling the abundance thereof comprising subjecting an evaporant material to electron bombardment heating in a high-vacuum electron beam furnace by injecting a beam of high-velocity electrons by an electron gun onto the surface of said evaporant material thereby causing vapor particles of such material to emanate from said surface, ionizing a portion of the particles of vapor by the action of electrons in said beam such that light is emitted having a frequency characteristic of the elemental constitution of the vapor and having an intensity dependent upon the density of the vapor, passing a portion of said emitted light through a light pipe disposed in optical communication with said vapor, filtering said passed light such that light of predetermined frequency is transmitted, detecting said transmitted light by producing an electrical signal systematically related to the intensity of the transmitted light, and utilizing said electrical signal to control the intensity of the electron beam from said electron gun, thereby maintaining the abundance of vapor at a predetermined level. 